Network Administration: Top-Level Domains

A top-level domain appears immediately beneath the root domain. Top-level domains come in two categories: generic domains and geographic domains. These categories are described in the following sections.

Generic domains

Generic domains are the popular top-level domains that you see most often on the Internet. Originally, seven top-level organizational domains existed. In 2002, seven more were added to help ease the congestion of the original seven — in particular, the com domain.

The following table summarizes the original seven generic top-level domains. Of these, you can see that the com domain is far and away the most populated, with nearly 1.9 million second-level domains beneath it.

The Size column in this table indicates approximately how many second-level domains existed under each top-level domain as of January 2007, according to an Internet Software Consortium survey.

The Original Seven Top-Level Domains
Domain Description Size
com Commercial organizations 1,291,296
edu Educational institutions 3,873
gov U.S. government institutions 966
int International treaty organizations 119
mil U.S. military institutions 110
net Network providers 253,741
org Noncommercial organizations 140,968

Because the com domain ballooned to an almost unmanageable size in the late 1990s, the Internet authorities approved seven new top-level domains in an effort to take some of the heat off of the com domain. Most of these domains, listed in the following table, became available in 2002. As you can see, they haven’t really caught on yet even though they’ve been around for several years.

The New Seven Top-Level Domains
Domain Description Size
aero Aerospace industry 147
biz Business 11,399
coop Cooperatives 263
info Informational sites 16,276
museum Museums 11
name Individual users 710
pro Professional organizations 30

Geographic domains

Although the top-level domains are open to anyone, U.S. companies and organizations dominate them. An additional set of top-level domains corresponds to international country designations. Organizations outside the United States often use these top-level domains to avoid the congestion of the generic domains.

The following table lists those geographic top-level domains with more than 200 registered subdomains at the time of this writing, in alphabetical order. In all, about 150 geographic top-level domains exist. The exact number varies from time to time as political circumstances change.

Geographic Top-Level Domains with More Than 200 Subdomains
Domain Description Domain Description
ac Ascension Island hu Hungary
ae United Arab Emirates ie Ireland
ag Antigua and Barbuda in India
am Armenia is Iceland
an Netherlands Antilles it Italy
as American Samoa jp Japan
at Austria kz Kazakhstan
be Belgium la Lao People’s Democratic Republic
bg Bulgaria li Liechtenstein
br Brazil lk Sri Lanka
by Belarus lt Lithuania
bz Belize lu Luxembourg
ca Canada lv Latvia
cc Cocos (Keeling) Islands ma Morocco
ch Switzerland md Moldova
cl Chile nl Netherlands
cn China no Norway
coop Cooperatives nu Niue
cx Christmas Island pl Poland
cz Czech Republic pt Portugal
de Germany ro Romania
dk Denmark ru Russian Federation
ee Estonia se Sweden
es Spain si Slovenia
eu European Union sk Slovakia
fi Finland st Sao Tome and Principe
fm Micronesia su Soviet Union
fo Faroe Islands to Tonga
fr France tv Tuvalu
ge Georgia tw Taiwan
gov Government ua Ukraine
gr Greece us United States
hr Croatia ws Samoa